import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 *   public ListNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution4 {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param head ListNode类 
     * @return ListNode类
     */
    public ListNode oddEvenList (ListNode head) {
        // write code here
        ListNode fast = head;
        ListNode slow = head;
        while(fast != null && slow != null) {
            //是奇数，fast就走，走到是偶数为止
            while(fast != null && fast.val % 2 != 0) {
                fast = fast.next;
            }
            //是偶数，slow就走，走到是奇数为止
            while(slow != null && slow.val % 2 == 0 || slow == head) {
                slow = slow.next;
            }
            if(fast != null && slow != null && fast.val % 2 == 0 && slow.val % 2 != 0) {
                int val = fast.val;
                fast.val = slow.val;
                slow.val = val;
                fast = fast.next;
                slow = slow.next;
            }
            
        }
        return head;
    }
}